The present invention relates to devices for converting between linear motion and rotary motion, and, more particularly, to a method for creating a "conjugated surface" from a "conjugate surface" for a device that converts between linear motion and rotary motion according to particular parameters of motion transfer. A "conjugate surface" has a tracking profile that either tracks or is tracked by the profile of a "conjugated surface" during motion conversion.
U.S. Pat. No. 5,259,256, to Douglas C. Brackett, one of the inventors of this invention, discloses a motion conversion device which translates linear motion to rotary motion using a conjugate-driver. A "conjugate-driver" component engages a "conjugate-bearing" without any clearance between the mechanical components throughout their full range of motion. As the engagement occurs along tracking and trackable profiles or "undulations," linear motion converts to rotary motion.
In one embodiment, this is implemented by the motion conversion device shown in FIG. 1. The conjugate drive mechanism includes a pair of conjugate-drivers 10 and 15 and a shuttle 20 containing a pair of conjugate-bearings that moves in a includes an aperture 25 with two sides. One side is defined by a first trackable profile 30 corresponding to the first conjugate-bearing, and the opposite side is defined by a second trackable profile 35 corresponding to the second conjugate-bearing. One of the conjugate-drivers 10 has a surface of a first tracking profile 40 having the same circumferential length as the first trackable profile 30. The other conjugate-driver 15 has a surface of a second tracking profile 45 having the same circumferential length as the second trackable profile 35. The "circumferential length" of a profile or a surface is to the total circumference of the curved portions that make up the profile or surface.
The conjugate drive mechanism also includes a rotatable crankshaft 50 having a crankpin, positioned within the aperture 25 of the shuttle, that revolves in a circular path. The two conjugate-drivers 10 and 15 are rotatably mounted on the crankpin 50. The first and second tracking profiles 40 and 45 on the conjugate-drivers engage the first and second trackable profiles 30 and 35 of the first and second conjugate-bearings, respectively, in a continuous conjugating manner as the crankpin revolves in the circular path. In this way the reciprocating rectilinear motion of the shuttle is continuously converted into the rotary motion of the crankshaft.
By manipulating the tracking and trackable profiles and their profiles, a system designer may control aspects of the operation of the motion conversion device. For example, in a piston engine, the designer may set the location of the peak position of the pistons, the stroke length of the pistons, the location of piston peak velocity, piston mean velocity, piston acceleration and deceleration, and piston dwell at top and bottom.
Prior to this invention, the only way to create a tracking profile and a trackable profile was by trial and error. A designer would create one surface to provide a desired set of parameters, and would approximate a matching surface based upon his or her best guess as to the proper shape. Using the approximation, the designer runs tests or simulations and iteratively modifies the design of the matching surface to engage the first surface in a continuous conjugating manner.
This trial and error process, however, is inefficient, time consuming, and prone to error. To use a different set of parameters for motion transfer, the designer would have to create a whole new first profile surface and engage in the trial and error process again to ensure the design of a proper matching profile surface. This severely limits the flexibility of the conjugate-driver and the conjugate-bearing in a device for motion transfer by imposing a very high initial cost on any new system design, and makes it difficult to design corresponding tracking trackable profiles.
It is desirable, therefore, to devise a manner in which to create the corresponding tracking and trackable profile surfaces quickly and efficiently.